The electricity storage device cell including electrodes wound in flat and stored in a container includes cells such as the electric double-layer capacitor, the lithium ion battery, and the lithium ion capacitor.
The electric double-layer capacitor includes polarizable electrodes (cathode and anode) facing each other on both sides of a separator, and utilizes an electrostatic capacity of electric double layers formed on surfaces of the polarizable electrodes in an electrolyte.
Moreover, the lithium ion battery includes a cathode made of an oxide of cobalt, nickel, manganese, or the like and an anode made of carbon, and has an advantage in that lithium can be stably charged and stored in the carbon anode.
Moreover, the lithium ion capacitor is being developed as a novel electric double-layer capacitor. The lithium ion capacitor is constructed by an electric double-layer capacitor having an anode doped with lithium ions, and has a characteristic that while an upper limit voltage higher than the electric double-layer capacitor is provided, a lower limit voltage cannot be reduced to 0 V.
Those electricity storage device cells are stored in a sealed container such as an aluminum-laminated container or a metal container, and can thus be constructed inexpensively and compactly. However, the output voltage is as low as approximately 3-4 V and is lower than the rating voltage of the aluminum electrolytic capacitor, which is 400 V, and those electricity storage device cells are thus generally used as a module formed by serially connecting the electricity storage device cells, thereby increasing the output voltage.
Electrodes used for the flat-wound electricity storage device cells are formed by applying a cathode electrode layer and an anode electrode layer respectively on a cathode collector foil and an anode collector foil in a strip shape having a thickness of approximately 10 to 30 μm, and winding several meters to several tens of meters of the cathode collector foil and the anode collector foil along with a porous separator in a strip shape made of a cellulose-based or olefin-based resin fabric therebetween about a winding shaft core in a flat shape.
The flat-wound electricity storage device cell constructed in this way allows winding in a short period, and is thus advantageous in mass-productivity and a low cost compared with an electricity storage device cell of a layered type constructed by laminating several tens of electrodes in a rectangular shape.
Note that, the winding shaft core is often used only for the flat winding, and is pulled out from a completed cell. However, if the winding shaft core is left, a winding shaft core in a hollow pipe shape made of a metal such as aluminum or the like or a resin is used.
It is expected that the flat-wound electric double-layer capacitor and lithium ion capacitor be applied to storage of regenerative energy from a motor from an energy saving viewpoint, and if they are used for brake regeneration on a servo motor, a hoisting machine for an elevator, and an electric train, and motor regeneration on a hybrid vehicle and the like, a feature of repeated charge/discharge of a large current exceeding 100 A is required.
If a large current flows, a power loss proportional to the square of the current and the internal resistance is generated, resulting in a degraded charge/discharge efficiency. Moreover, this power loss directly translates into generated heat, and unless the heat is quickly radiated from the collector foils, which are thermal conductors, the temperature increases inside the electricity storage device cell, the performance quickly decreases, and lifetime degradation and the like occur.
In particular, the electrode expands and absorbs the electrolyte, and deficiency of the electrolyte tends to occur, causing accelerated degradation during the charge. Therefore, it is necessary for realizing quick charge/discharge in the flat-wound electricity storage device to greatly increase the heat radiation property from the collector foils, and to greatly decrease collector resistances for preventing the heat generation. The collector resistances as used herein mean electric resistances from the collector foils of the cathode and anode to respective current terminals.
In the conventional flat-wound electricity storage device cell that has been used, a cathode collector foil and an anode collector foil are protruded from separators in directions opposite to each other with respect to the axial direction of winding, cutoff portions and protruded end portions are formed by partially cutting off peripheral portions on which a cathode electrode layer and an anode electrode layer are not formed so as to expose the separators, and the cathode collector foil and the anode collector foil are respectively electrically connected at the protruded end portions in the laminated direction, and are respectively connected electrically to a cathode terminal and an anode terminal.
Moreover, in the flat-wound electricity storage device module that has been used, a plurality of the electricity storage device cells are arranged so that the cathode terminal of an electricity storage device cell and the anode terminal of another neighboring electricity storage device cell are close to each other, and the cathode terminal and the anode terminal are connected by a electrically conductive radiator plate (see Patent Literature 1).